The present invention relates to a Diesel engine electromagnetic fuel injector of straightforward, compact design and a high degree of reliability.
Injectors of this type usually comprise a plunger sliding inside the injector body, for controlling fuel passage between an injection chamber, supplied with fuel under pressure, and at least one injection orifice formed in an injection nozzle secured to the body; and an electromagnetic fuel metering valve for controlling fuel passage through a drain orifice between a control chamber, supplied with fuel under pressure, and a low-pressure chamber, and reducing the pressure of the fuel in said chamber by draining the same through said orifice.
Appropriate surface portions of the plunger are exposed to the fuel inside the injection and control chambers, so that the pressures inside the same and exerted on said surface portions raise the plunger when the pressure inside the control chamber falls to a given value, thus enabling fuel supply through the injection orifices on the nozzle.
Injectors of the type briefly described above present a number of drawbacks.
Firstly, they are extremely complex in design and of large size, particularly radially. In fact, for feeding pressurized fuel into the control and injection chambers, two separate fittings are provided, each connected to a respective delivery line. Moreover, two ducts are required inside the injector for respectively connecting said fittings to the injection and control chambers. As a result of the injection chamber being located at the bottom of the injector, the first of said ducts is extremely long and comprises a number of portions formed in various parts of the injector. For forming both said ducts, therefore, numerous holes and cavities must be formed inside the injector body and connected members. Moreover, additional holes must be provided for housing the plunger, some of which must be appropriately ground for ensuring correct guiding of the plunger during its movement.
A further drawback of injectors of the aforementioned type is that they fail to provide for accurate metering of the fuel, especially when operated frequently. This is often caused by malfunctioning of the fuel metering valve as a result of incorrect operation of the anchor forming part of the valve and controlling displacement of the plugging member on the same. Said anchor, in fact, is not always guided accurately during its movement, and often contacts the core of the electromagnet facing it.